Gabapentin and sexual dysfunction: an overlooked and underreported problem?

Association between erectile dysfunction and fibromyalgia in male patients: A Taiwanese nationwide population-based cohort study

OBJECTIVES

To investigate the association between erectile dysfunction and fibromyalgia, and to clarify related comorbidities and treatment modalities.

METHODS

This retrospective cohort study was carried out using 1 million records in the National Health Insurance Research Database. From 2001 to 2012, a total of 53 678 male patients newly diagnosed with fibromyalgia were recruited as the fibromyalgia cohort, and the same number of the non-fibromyalgia cohort was enrolled and matched with propensity score with age, income, comorbidities, and prescribed medications. All records were followed up until the end of 2013. The Cox proportional hazards model was carried out to assess the risk of erectile dysfunction among fibromyalgia patients.

RESULTS

The incidence rates of erectile dysfunction were 36.86 and 21.15 (per 10 000 person-years) in the fibromyalgia and non-fibromyalgia cohorts, respectively, and a significantly increased risk of erectile dysfunction in fibromyalgia patients was noted (adjusted hazard ratio 1.69, 95% confidence interval 1.55-1.85, P < 0.001). The Cox proportional hazards regression analysis showed increased risk of erectile dysfunction in the fibromyalgia cohort regardless of treatment prescriptions of tramadol, antidepressants, gabapentin and non-steroidal anti-inflammatory drugs.

CONCLUSIONS

Fibromyalgia was found to be an independent risk factor for the incidence of erectile dysfunction.

Implications and mechanism of action of gabapentin in neuropathic pain

Gabapentin is an anti-epileptic agent but now it is also recommended as first line agent in neuropathic pain, particularly in diabetic neuropathy and post herpetic neuralgia. α2δ-1, an auxillary subunit of voltage gated calcium channels, has been documented as its main target and its specific binding to this subunit is described to produce different actions responsible for pain attenuation. The binding to α2δ-1 subunits inhibits nerve injury-induced trafficking of α1 pore forming units of calcium channels (particularly N-type) from cytoplasm to plasma membrane (membrane trafficking) of pre-synaptic terminals of dorsal root ganglion (DRG) neurons and dorsal horn neurons. Furthermore, the axoplasmic transport of α2δ-1 subunits from DRG to dorsal horns neurons in the form of anterograde trafficking is also inhibited in response to gabapentin administration. Gabapentin has also been shown to induce modulate other targets including transient receptor potential channels, NMDA receptors, protein kinase C and inflammatory cytokines. It may also act on supra-spinal region to stimulate noradrenaline mediated descending inhibition, which contributes to its anti-hypersensitivity action in neuropathic pain.